Artificial Muscles May Pave Way for Superhuman Exoskeletons, Robots

Published on February 26, 2014

Newly engineered thermal-powered artificial muscles, created from fishing line and sewing thread, may have a variety of future applications including in superhuman exoskeletons and humanoid robot companions for older adults. The artificial muscles can lift 100 times more weight and generate 100 times higher mechanical power than human muscles of the same length and weight, developers say.

According to the University of Texas at Dallas (UT Dallas), an international team of researchers from universities in Australia, South Korea, Canada, Turkey, and China teamed up with the university’s own Alan G. MacDiarmid Nano Tech Institute scientists to develop the muscles. A paper appearing in the journal Science notes that the muscles are produced by twisting and coiling high-strength polymer fishing line and sewing thread.

UT Dallas reports in a recent news release that the muscles are powered thermally by temperature changes, which can be facilitated either electrically, by the absorption of light, or by the chemical reaction of fuels. The researchers note that by twisting the polymer fiber, it converts it to a torsional muscle that can spin a heavy rotor to more than 10,000 revolutions per minute. The subsequent twisting allows the polymer fiber to coil and produce a muscle that contracts along its length when heated and returns to its initial length when cooled. The release states that if coiling is in a different twist direction than the initial polymer fiber twist, the muscles expand when heated.

The release adds that compared to natural muscles, which contract by about 20%, these new muscles can contract by about to 50% of their length. Ray Baughman, PhD, corresponding author, and the Robert A. Welch Distinguished Chair in Chemistry at UT Dallas, director of the Nano Tech Institute, calls the applications for the polymer muscles “vast.”

The muscles, he adds, could be used to produce superhuman strength in applications that include exoskeletons and robots. By twisting together a bundle of polyethylene fishing lines with a diameter about 10 times larger than a human hair, a coiled polymer muscle can be produced that can lift 16 pounds. When operated in parallel, Baughman says, 100 of these polymer muscles could lift about 1,600 pounds. The release notes that independently operated coiled polymer muscles with a diameter less than a human hair may provide the opportunity for lifelike facial expressions to humanoid companion robots for older adults and dexterous capabilities for minimally invasive robotic microsurgery. They could also hold promise in devices designed to communicate the sense of touch from sensors on a remote robotic hand to a human hand.

Lead author of the study Carter Haines, doctoral student in materials science and engineering, says while the polymer muscles are normally electrically powered by resistive heating using metal coating on sewing thread or by using metal wires twisted together with the muscle, in other applications the muscles can be self-powered by environmental temperature changes.

Additionally, “We have woven textiles from polymer muscles whose pores reversibly open and close with changes in temperature. This offers the future possibility of comfort-adjusting clothing,” Haines says.

The researchers state that they have also demonstrated the feasibility of using environmentally powered muscles to automatically open and close windows of greenhouses or buildings in response to ambient temperature changes, eliminating the need for electricity or motors.